TC4钛合金铣削亚表面损伤形成机制及其对疲劳性能影响规律研究

Subsurface damages in the milling of TC4 titanium alloy is one of the key factors affecting the fatigue property of parts. However, the formation mechanism of subsurface damages and its influence on fatigue property are not still studied thoroughly. As a result, the actual fatigue life of TC4 titanium alloy parts is far below the design requirement. In this project, a new method called grazing incidence X-ray diffraction (GIXD) is introduced to nondestructively test and analyze the milling subsurface of TC4 titanium alloy, which will be used to reveal the microstructure and gradient distribution of subsurface damages. Based on dislocation dynamics and phase transformation thermodynamics, the generation and evolution of different damages are studied to clarify the formation mechanism of subsurface damages under external stresses. The variation of stress state in the front and bottom of cutting edge during milling TC4 titanium alloy is analyzed by finite element simulation. By combining the formation mechanism of subsurface damages, critical stress conditions for the generation and evolution of damages are established, which provides theoretical basis to control subsurface damage. The residual stress and intrinsic mechanical properties in subsurface are obtained by GIXD and nanoindentation experiments. On this basis, the fatigue property are evaluated comprehensively by damage mechanics and fracture mechanics to reveal the influence mechanism and regularity of subsurface damages on fatigue property. This research has important significance for improving the fatigue life of TC4 titanium alloy parts and ensuring the reliability of aero-engine.

TC4钛合金铣削亚表面损伤是影响零件疲劳性能的关键因素之一。然而，目前对亚表面损伤形成机制及其对疲劳性能影响规律还缺少深入研究，导致TC4钛合金零件实际的疲劳寿命还远低于设计指标要求。本项目引入掠入射X射线衍射（GIXD）新方法对TC4钛合金铣削亚表面进行无损检测分析，以揭示亚表面损伤的微观形式及梯度分布规律；基于位错动力学、相变热力学研究不同损伤的生成与演变规律，从而阐明在外应力作用下亚表面损伤形成机制；利用有限元仿真分析TC4钛合金铣削过程刀刃前下方应力状态变化规律，结合亚表面损伤形成机制建立损伤生成与演变的临界应力条件，为控制亚表面损伤提供理论依据。通过GIXD和纳米压痕实验获得亚表面的残余应力和本征力学性能后，运用损伤力学和断裂力学综合评价疲劳性能，以揭示亚表面损伤对疲劳性能的影响机制与规律。研究成果对提高TC4钛合金零件疲劳寿命，保证航空发动机可靠性具有重要意义。

TC4钛合金铣削导致的亚表面损伤是影响零件疲劳性能的关键因素之一。如何控制TC4钛合金铣削亚表面损伤是提高零件疲劳性能的关键问题。因此，迫切需要弄清TC4钛合金铣削亚表面损伤的形成机制，揭示亚表面损伤对疲劳性能的影响机制与规律。本研究掌握了TC4钛合金铣削亚表面损伤的微观形式，揭示了亚表面损伤沿深度方向的梯度分布规律，阐明了亚表面损伤形成机制，建立了铣削工艺对亚表面损伤的影响规律，获得了TC4钛合金不同铣削工艺条件下刀刃前下方区域应力状态的变化规律，掌握了该区域剪应力和主应力的分布特征，结合亚表面损伤形成机制建立了损伤生成与演变的临界应力条件，获得了TC4钛合金铣削表面/亚表面的显微硬度分布规律，建立了亚表面损伤深度预测模型。本项目研究成果对实现钛合金叶片的高表面完整性加工具有重要指导意义，对提高航空发动机的服役安全具有重要工程价值。